Variable-area fuel injectors have been used in many applications relating to air-breathing propulsion systems, including, for example, in ramjets, scramjets, and in gas turbine engines such as those used in aviation. Ramjets, scramjets, and gas turbine engines typically include a section for compressing inlet air, a combustion section for combusting the compressed air with fuel, and an expansion section where the energy from the hot gas produced by combustion of the fuel is converted into mechanical energy. The exhaust gas from the expansion section may be used to achieve thrust or as a source of heat and energy.
Generally, some type of fuel injector is used in the combustion section for spraying a flow of fuel droplets or atomized fuel into the compressed air to facilitate combustion. In some applications of air-breathing propulsion systems including ramjets, scramjets, and particularly in gas turbine engines, which must run at variable speeds, variable-area fuel injectors have been used because they provide an inexpensive method to inject fuel into a combustor, while also metering the fuel flow without the need for an additional metering valve.
Typically, the fuel flow rate is controlled by the combination of a spring, the fuel pressure, and an annular area, which is increasingly enlarged as the fuel pressure is increased. This is unlike the operation of pressure-swirl atomizers where the pressure-flow characteristics are static, and are determined solely by the fixed injector geometry and the variable injection pressure. Generally, variable-area fuel injectors provide good atomization over a much wider range of flow rates than do most pressure-swirl atomizers. Additionally, with variable-area fuel injectors, the fuel pressure drop is taken at the fuel injection location, thus providing better atomization than typical pressure-swirl and plain-orifice atomizers.
However, throughout its operational pressure range, most variable-area fuel injectors do not provide optimal spray circumferential uniformity, or patternation. Typically, these conventional variable-area fuel injectors have slots or holes used to feed fuel to the fuel manifold which is upstream of the exit area. In general, this configuration does not prevent the formation of wakes in the fuel flow downstream of these slots or holes. Optimal patternation is desirable in order to avoid non-uniform fuel distribution, which can cause hot spots in air-breathing engines resulting in thermal distress and failure of the engine itself. Good patternation also helps avoid regions of high fuel concentration (i.e., rich regions) in combustors, which reduces fuel efficiency and leads to poor emissions quality.
In applications not related to air-breathing engines, poor patternation can also lead to failure of the device. One such application is the automotive engine exhaust treatment process in which fuel is used to increase the temperature of the engine exhaust. By increasing the temperature of the exhaust, downstream post-engine exhaust treatment devices, such as dosers and diesel particulate filters can operate more effectively. However, poor patternation can cause hot-spots in the matrix of both the doser and the diesel particulate filter, thus reducing the life of the matrix.
Therefore, it would be desirable to have a variable-area fuel injector that provides superior patternation throughout the operational fuel flow range. Embodiments of the invention provide such a variable-area fuel injector. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.